1. Field of the Invention
This invention relates generally to battery chargers, and in particular to the battery chargers for small storage batteries in appliances, small motorized vehicles and equipment installed in fields or other remote locations.
2. Description of the Prior Art
In recent years there has been a greater use of small, but powerful low current storage batteries in lawn-mowers, lawn-tractors, solar recharged fence chargers, in-field radio transmitting equipment, and motorcycles. These batteries are generally of the liquid cell and jell cell type. In the past, the only manufacture recommended way to recharge these small batteries, was to bring the discharged battery to an AC source, and hook-up to a small, often expensive charger, until the discharged battery was recharged.
Commonly when a storage battery is discharged, there is no convenient AC source nearby. Consequently, one is faced with the choice of transporting often bulky pieces of equipment to an AC source or removing the battery, transporting the battery to an AC source and reinstalling it or jumping the battery from another battery with jumper cables. The prior art alternatives were often impractical, inconvenient or dangerous. Often the battery powered equipment was bulky or permanently installed in a remote location. Thus, moving the equipment could be time consuming and inconvenient. Similarly, removal of the battery for transportation to an AC source can also be time consuming and inconvenient. Moreover, the equipment will be inoperative during the time the battery is removed unless a temporary replacement is available. Jumping the small battery with conventional jumper cables is also unsatisfactory. Such cables are directly connected to the battery terminal, with the connection of the last connector to a terminal, the final hookup. In the use of conventional jumper cables, there is a danger of a large current surge which can melt the internal contacts of the battery and possibly cause an explosion with resulting damage to person and property. Typically these storage batteries require a charging rate of between 0.5 amp to 3 amps. When the charging rate exceeds 6 amps, on a 30 amp-hour battery, there is a danger of a melting of the internal contacts and an explosion of the storage battery. When the charging rate exceeds 25% of the battery amp-hours of some small batteries, you begin to risk internal construction parts damage to the battery. For instance, a 30 amp-hour battery could have a charging range of 0-7.5 amps with an average range of 3 amps. This tolerance allows for short current surges that can occur at charging and attempting to start a motorized vehicle at the same time. Another problem with jumper cables is there is often a spark generated at the terminals during final connection of the last cable. Such sparks can ignite the gasses given off at the battery terminals thus producing an explosion.
Prior art battery chargers have been proposed. For example, U.S. Pat. No. 4,258,305 provides an emergency battery charger for vehicles having cigarette lighters. A cigarette lighter plug is provided for engagement in the cigarette lighter of each vehicle. The plugs are connected by a conductor having a light connected thereto between the two cigarette lighter plugs. U.S. Pat. No. 4,464,402 provides jumper cables with circuitry located between the connectors which prevents damage to the battery as a result of reverse or cross connection of the cables or shorting of the connectors.